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CN113969336B - Method for manufacturing hot-dip galvanized steel sheet, steel sheet and vehicle member - Google Patents

Method for manufacturing hot-dip galvanized steel sheet, steel sheet and vehicle member Download PDF

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Publication number
CN113969336B
CN113969336B CN202010720177.4A CN202010720177A CN113969336B CN 113969336 B CN113969336 B CN 113969336B CN 202010720177 A CN202010720177 A CN 202010720177A CN 113969336 B CN113969336 B CN 113969336B
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Prior art keywords
steel sheet
atmosphere
heating
soaking
steel plate
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CN113969336A (en
Inventor
金鑫焱
钟勇
陈孟
李旭飞
王利
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Priority to CN202010720177.4A priority Critical patent/CN113969336B/en
Application filed by Baoshan Iron and Steel Co Ltd filed Critical Baoshan Iron and Steel Co Ltd
Priority to US18/017,057 priority patent/US20230295758A1/en
Priority to CA3186254A priority patent/CA3186254A1/en
Priority to PCT/CN2021/103136 priority patent/WO2022017138A1/en
Priority to JP2023504450A priority patent/JP2023534861A/en
Priority to KR1020237005437A priority patent/KR20230043138A/en
Priority to EP21846555.7A priority patent/EP4186986A4/en
Priority to TW110126541A priority patent/TWI780824B/en
Publication of CN113969336A publication Critical patent/CN113969336A/en
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Coating With Molten Metal (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

The invention provides a method for manufacturing a hot dip galvanized steel sheet, which comprises the steps of carrying out heat treatment, hot dip coating and alloying treatment on the steel sheet with high Si and Mn content, wherein the heat treatment step comprises a first heating stage and a soaking stage, wherein the first heating atmosphere of the first heating stage contains 0.01-0.5% of O by volume fraction 2 The remainder being N 2 And unavoidable impurities, the soaking atmosphere in the soaking stage containing more than 0.5% by volume of H 2 The balance being N 2 And inevitable impurities, and controlling the dew point of the first heating atmosphere and the soaking atmosphere to be more than or equal to-20 ℃. The invention also provides a hot-dip galvanized steel sheet and a vehicle member. According to the invention, by controlling the heat treatment atmosphere, the enrichment of Si and Mn alloy elements on the surface of the steel plate and the interface of iron oxide and the interface of reduced iron and the base steel plate is inhibited, so that when the hot-dip galvanized steel plate adopts a steel plate with high Si and Mn content as a base material, sufficient coating Fe content and high fracture elongation can be obtained after the alloying treatment step.

Description

Method for manufacturing hot-dip galvanized steel sheet, steel sheet and vehicle member
Technical Field
The present invention relates to a metal working method and a product thereof, and particularly to a method for producing a hot-dip galvanized steel sheet, a steel sheet, and a vehicle member.
Background
In recent years, there has been a growing demand for hot-dip galvanized steel sheets in the fields of automobiles, home appliances, building materials, and the like, and a method for producing the hot-dip galvanized steel sheets includes subjecting the steel sheets to reduction annealing, hot dip plating, and alloying treatment in this order. In the reduction annealing stage, individual oxidation points of the steel sheet are reduced, and the steel sheet is formed into an austenite structure at a high temperature and retains a part of austenite (i.e., retained austenite) after the annealing is completed to increase the fracture elongation of the steel sheet, and in the hot dip coating stage, a pure zinc coating layer is formed on the steel sheet, and in the alloying treatment stage, zn of the coating layer and Fe of the steel sheet are diffused with each other, so that the coating layer obtains a sufficient Fe content, and a zinc-iron alloy coating layer is formed. After alloying treatment, the hot dip galvanized steel sheet obtains reliable and excellent antirust performance by a plating layer which is not easy to fall off, thereby obtaining wide and large-scale application.
At present, in order to improve the tensile strength of a hot-dip galvanized steel sheet, it is proposed to use a steel sheet with high Si and Mn contents as a base material of the hot-dip galvanized steel sheet, but Si and Mn alloying elements are concentrated on the surface of the steel sheet in the form of continuous oxides during the reduction annealing process, and thus the diffusion of zinc and iron is hindered, thereby affecting the alloying speed. If the alloying temperature and time are not changed, the Fe content of the coating of the alloyed steel plate is insufficient. If the alloying temperature is increased or the alloying time is prolonged in order to ensure the Fe content of the plating layer, the stability of the residual austenite is destroyed, the proportion of the residual austenite in the structure of the hot-dip galvanized steel sheet is reduced, and the fracture elongation of the hot-dip galvanized steel sheet is reduced.
Patent document CN101809182B provides a method for preparing a hot dip galvannealed steel sheet, comprising the steps of: -oxidizing the steel sheet so as to form an iron oxide layer on the surface of the steel sheet, and forming an internal oxide of at least one oxide selected from the group consisting of: si oxide, mn oxide, al oxide, a composite oxide containing Si and Mn, a composite oxide containing Si and Al, a composite oxide containing Al and Mn, and a composite oxide containing Si, mn, and Al; reducing the oxidized steel sheet to reduce the iron oxide layer; -hot dip galvanising the reduced steel sheet to form a zinc-based coated steel sheet; and subjecting the zinc-based coated steel sheet to an alloying treatment to form a galvannealed steel sheet. The Fe content of the plating layer of the steel sheet is insufficient or the elongation at break of the steel sheet is too low.
As described above, in the prior art, when a steel sheet having high Si and Mn contents is selected as a base material for a hot-dip galvanized steel sheet, it is difficult to obtain a sufficient Fe content in a plating layer and a high elongation at break at the same time after alloying treatment.
Disclosure of Invention
The inventors found that the iron oxide layer formed by the conventional method has a certain effect of inhibiting the enrichment of Si, mn alloying elements on the surface of the steel sheet, but this method brings a new problem that the iron oxide layer and the reduced iron layer form interfaces with the base steel sheet, respectively, and the internal oxides formed by the Si, mn alloying elements are enriched at the interface between the iron oxide layer and the base steel sheet and at the interface between the reduced iron layer and the base steel sheet, and during the alloying process, the range of zinc and iron diffusion includes both the surface of the steel sheet and the interface between the reduced iron layer and the base steel sheet, thereby affecting the alloying speed, so that the coating Fe content of the steel sheet is insufficient or the elongation at break of the steel sheet is too low.
In view of the above problems, an object of the present invention is to provide a method for producing a galvanized steel sheet, which can suppress the enrichment of Si and Mn alloying elements not only on the surface of the steel sheet but also on the interface between iron oxide and the base steel sheet and the interface between reduced iron and the base steel sheet, so that when a steel sheet having a high Si and Mn content is selected as a base metal of the galvanized steel sheet, a sufficient Fe content in the plated layer and a high elongation at break can be obtained at the same time after the alloying step.
The inventors have made extensive studies to solve the above problems, and in the course of the study, they have found that the concentration of Si or Mn alloy elements at the interface between iron oxide and the base steel sheet and at the interface between reduced iron and the base steel sheet is influenced by the dew point, and that the concentration can be suppressed by increasing the dew point. Therefore, the inventor finds that in the process of firstly introducing oxygen for oxidation and then reducing hydrogen for steel plates, the dew point is controlled to be more than or equal to-20 ℃, so that the enrichment on the surfaces of the steel plates can be effectively inhibited, and the enrichment on the interfaces of iron oxide and the matrix steel plates and the enrichment on the interfaces of reduced iron and the matrix steel plates can be effectively inhibited, thereby completing the invention.
The invention provides a method for producing a hot-dip galvanized steel sheet, comprising the steps of subjecting a base steel sheet containing 0.5% by mass or more of Si and 0.5% by mass or more of Mn to a heat treatment step, a hot-dip plating step and an alloying treatment step, wherein the heat treatment step comprises a first heating stage and a soaking stage, and the first heating atmosphere of the first heating stage contains 0.01-0.5% by volume of O 2 The balance being N 2 And unavoidable impurities, the soaking atmosphere in the soaking stage containing more than 0.5% by volume of H 2 The balance being N 2 And unavoidable impurities, and controlling the dew point of the first heating atmosphere and the soaking atmosphere to be more than or equal to-20 ℃.
Optionally, the heat treatment step further comprises a second heating stage, wherein the second heating atmosphere of the second heating stage contains more than 0.5% of H by volume fraction 2 The balance being N 2 And unavoidable impurities, and controlling the dew point of the second heating atmosphere to be not less than-20 ℃.
Alternatively, the base steel sheet contains, by mass, 0.1 to 0.3% of C, 0.5 to 3.0% of Si, 0.5 to 4.0% of Mn, and the balance Fe and inevitable impurities.
Optionally, in the hot dip coating step, the temperature of the steel plate is 450-520 ℃ when the steel plate is put into a zinc pot, the temperature of the plating solution is 450-500 ℃, the plating solution contains 0.10-0.15% by mass of Al, and the balance of Zn and inevitable impurities, and the plating adhesion of each surface of the steel plate subjected to the hot dip coating step is 30-90g/m 2 。
Optionally, the temperature of the steel plate in the alloying treatment step is controlled to be less than or equal to 500 ℃ and the time is controlled to be less than or equal to 25 seconds.
Optionally, the temperature of the steel plate in the alloying treatment step is controlled to be more than or equal to 460 ℃, and the time is controlled to be more than or equal to 5 seconds.
Optionally, the outlet temperature of the first heating stage is controlled to be in the range of 570-750 ℃.
Optionally, the temperature of the steel plate in the soaking stage is controlled to be 750-930 ℃ for 30-300 seconds.
Optionally O of the first heating atmosphere 2 The volume fraction is 0.03-0.3%.
Optionally, H of a second heating atmosphere, soaking atmosphere 2 The volume fraction is less than or equal to 10 percent.
Optionally, the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are controlled to be less than or equal to 30 ℃.
Optionally, the dew point of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere is controlled to be more than or equal to-10 ℃.
Optionally, the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are controlled to be more than or equal to 0 ℃.
A second object of the present invention is to provide a hot-dip galvanized steel sheet that has a steel sheet with high Si and Mn contents as a base material and that can achieve both a sufficient Fe content in the plated layer and a high elongation at break after an alloying step.
In order to achieve the above object, the present invention also provides a hot-dip galvanized steel sheet produced by the above production method.
Optionally, the steel plate comprises a zinc-iron alloy coating and an internal oxidation layer from outside to inside, the zinc-iron alloy coating contains 7-13% of Fe by mass, the proportion of the retained austenite phase in the structure is more than or equal to 5%, the tensile strength of the steel plate is more than or equal to 980MPa, and the fracture elongation is more than or equal to 20%.
A third object of the present invention is to provide a vehicle component that meets the performance requirements of the vehicle component.
In order to achieve the above object, the present invention also provides a member for a vehicle, which is made of the above hot-dip galvanized steel sheet.
According to the method for manufacturing the hot-dip galvanized steel sheet, provided by the invention, the heat treatment atmosphere is controlled, so that the enrichment of Si and Mn alloy elements on the surface of the steel sheet is inhibited, the enrichment of Si and Mn alloy elements on the interface of iron oxide and a base steel sheet and the interface of reduced iron and the base steel sheet are inhibited, when the steel sheet with high Si and Mn content is selected as a base metal of the hot-dip galvanized steel sheet, the proper temperature and time of the steel sheet can be selected in the alloying treatment step, and the sufficient Fe content of a coating and the high elongation at break can be obtained.
Drawings
FIG. 1 is a schematic view of a temperature control curve of the manufacturing method of the present invention.
Fig. 2 is a schematic cross-sectional view of a steel sheet after each step of the manufacturing method provided by the present invention.
FIG. 3 is a metallographic photograph of a cross section of a hot-dip galvanized steel sheet obtained in example 1.
FIG. 4 is a metallographic photograph showing a cross section of a hot-dip galvanized steel sheet obtained in comparative example 7.
Reference numerals
(a) No step was performed; (b) after the first heating stage; (c) after the second heating stage and the soaking stage; (d) after the hot dip coating step; and (e) alloying.
1. A base steel plate; 1'. Base steel plate; 2. an internal oxide layer; 3. iron oxide; 4. reducing iron; 5. pure zinc plating; 6. and (4) zinc-iron alloy coating.
Detailed Description
The following description is given by way of example of the present invention and other advantages and features of the present invention will become apparent to those skilled in the art from the following detailed description. While the invention will be described in conjunction with the preferred embodiments, it is not intended that the features of the invention be limited to that embodiment. On the contrary, the invention is described in connection with the embodiments for the purpose of covering alternatives or modifications that may be extended based on the claims of the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention.
The present invention provides a method for producing a hot-dip galvanized steel sheet, including a heat treatment step, a hot-dip coating step, and an alloying treatment step of a base steel sheet containing, by mass, 0.5% or more of Si and 0.5% or more of Mn. Heat treatment refers to a hot metal working process in which a material is heated, held and cooled in the solid state to achieve a desired texture and properties. Hot dip plating is a process method for forming a metal coating on the surface of a workpiece by immersing the workpiece in a molten metal bath, and in the technical scheme, a steel plate is immersed in a zinc bath to form a pure zinc coating on the surface of the steel plate. The alloying treatment in the technical scheme is that the steel plate is kept at a certain temperature, namely the steel plate temperature in the alloying treatment step, and the heat preservation time is the time in the alloying treatment step, so that the pure zinc coating becomes a zinc-iron alloy coating through mutual diffusion of iron elements in the steel plate and zinc elements in the pure zinc coating. The heat treatment step includes a first heating stage of heating the steel sheet from ambient temperature to a temperature, i.e., an exit temperature of the first heating stage, the heating atmosphere of the first heating stage being referred to as a first heating atmosphere, and a soaking stage of heating the steel sheet at a certain temperatureA heat preservation stage at the temperature, namely the temperature of the steel plate in the soaking stage, and the heat preservation time, namely the time in the soaking stage. Wherein the first heating atmosphere of the first heating stage contains 0.01-0.5% by volume of O 2 The balance being N 2 And inevitable impurities, the soaking atmosphere in the soaking stage contains more than 0.5% of H by volume fraction 2 The balance being N 2 And inevitable impurities, and controlling the dew point of the first heating atmosphere and the soaking atmosphere to be more than or equal to-20 ℃.
The dew point is a temperature at which the air is cooled to saturation, i.e., a temperature at which the water vapor and water reach an equilibrium state, under the condition that the water vapor content in the atmosphere is constant and the air pressure is kept constant.
After the first heating stage, O due to the first heating atmosphere 2 A layer of iron oxide is formed on the surface of the steel plate which can oxidize the base material, so that an internal oxidation layer formed by Si and Mn alloy elements is basically only arranged below the iron oxide, and the enrichment of the Si and Mn alloy elements on the surface of the steel plate in the first heating stage and the soaking stage is inhibited. Meanwhile, the high dew point enables an internal oxidation layer formed by Si and Mn alloy elements to be basically only present in the base steel plate below the iron oxide, but not on the interface of the iron oxide and the base steel plate, so that the enrichment of the Si and Mn alloy elements at the interface of the iron oxide and the base steel plate in the first heating stage is inhibited, and the high dew point also has a certain promotion effect on inhibiting the surface enrichment of the steel plate.
After the soaking stage, the iron oxide is soaked in H of the soaking atmosphere 2 Reducing the iron into reduced iron. In the soaking stage, an internal oxidation layer formed by the Si and Mn alloying elements is basically only present below the iron oxide which is not reduced yet and the reduced iron which is reduced from the iron oxide, so that the surface enrichment of the Si and Mn alloying elements on the steel sheet in the soaking stage is inhibited, the effect of inhibiting the surface enrichment of the steel sheet in the first heating stage is maintained, and the preparation is made for the subsequent hot dip plating. Meanwhile, the high dew point causes the thickness of the internal oxide layer in the base steel sheet to increase toward the inside of the base steel sheet, rather than toward the interface (where the interface includes the interface of iron oxide and the base steel sheet and the interface of reduced iron and the base steel sheet), i.e., the enrichment at the interface is suppressedThe effect of inhibiting the interface enrichment of the iron oxide and the matrix steel plate in the first heating stage is maintained, and the high dew point also has a certain promotion effect on inhibiting the surface enrichment of the steel plate.
When O is present 2 When the volume fraction of (b) is less than 0.01%, the oxidation degree of the base steel sheet is too low to sufficiently suppress the surface enrichment of the steel sheet; when O is present 2 When the volume fraction of (A) is more than 0.5%, the oxidation degree of the base steel sheet is too high, which is not favorable for subsequent reduction and coating adhesion. Thus defining O of the first heating atmosphere 2 The volume fraction is 0.01-0.5%.
When H is present 2 When the volume fraction is less than 0.5%, the reduction effect is insufficient, which is not favorable for subsequent hot dipping. Thus defining a soaking atmosphere of H 2 Volume fraction is more than or equal to 0.5 percent, when H 2 When the volume fraction is more than or equal to 2 percent, the reduction effect is better, so that the H in the soaking atmosphere 2 The volume fraction is preferably ≥ 2%.
When the atmosphere dew point is lower than minus 20 ℃, the enrichment of the iron oxide and the matrix steel plate and the enrichment of the reduced iron and the matrix steel plate at the interface are hardly inhibited in the first heating stage and the soaking stage, so that the dew points of the first heating atmosphere and the soaking atmosphere are limited to be more than or equal to minus 20 ℃.
Optionally, as shown in fig. 1, the heat treatment step further includes a second heating stage, the second heating stage is a stage of heating the steel sheet from the exit temperature of the first heating stage to the steel sheet temperature of the soaking stage, the heating atmosphere of the second heating stage is referred to as a second heating atmosphere, and the second heating atmosphere of the second heating stage contains H in a volume fraction of 0.5% or more 2 The balance being N 2 And inevitable impurities, and controlling the dew point of the second heating atmosphere to be more than or equal to-20 ℃.
The method for producing a hot-dip galvanized steel sheet further comprises a first cooling stage of cooling the steel sheet from the steel sheet temperature in the soaking stage to the steel sheet temperature when the steel sheet is placed in a zinc pot, and a second cooling stage of cooling the steel sheet from the steel sheet temperature in the alloying step to the ambient temperature.
After the first heating stage, as shown in FIG. 2, the cross-section of the steel sheet changes from that shown in FIG. 2 (a) to that shown in FIG. 2 (b), due to the first heating stageO of the atmosphere 2 A layer of iron oxide 3 is formed on the surface of the steel plate 1 which can oxidize the base material, so that an internal oxidation layer 2 formed by Si and Mn alloy elements is basically only arranged below the iron oxide 3, and the enrichment of the Si and Mn alloy elements on the surface of the steel plate in a first heating stage, a second heating stage and a soaking stage is inhibited. Meanwhile, the internal oxidation layer 2 formed by the Si and Mn alloy elements is basically only present in the base steel plate 1' below the iron oxide 3 instead of on the interface of the iron oxide 3 and the base steel plate 1', so that the enrichment of the Si and Mn alloy elements at the interface of the iron oxide 3 and the base steel plate 1' in the first heating stage is inhibited, and the high dew point also has a certain promotion effect on inhibiting the surface enrichment of the steel plate.
After the second heating step and the soaking step, the steel sheet has a cross section changed from that shown in FIG. 2 (b) to that shown in FIG. 2 (c), and the iron oxide 3 is heated in the second heating atmosphere and the soaking atmosphere in H 2 Reduced to reduced iron 4. In the second heating stage and the soaking stage, the internal oxidation layer 2 formed by the Si and Mn alloying elements is basically only present below the iron oxide 3 which is not reduced yet and the reduced iron 4 which is reduced from the iron oxide 3, so that the surface enrichment of the Si and Mn alloying elements on the steel plate in the second heating stage and the soaking stage is inhibited, the effect of inhibiting the surface enrichment of the steel plate in the first heating stage is maintained, and the preparation is made for the subsequent hot dip plating. Meanwhile, the thickness of the internal oxidation layer 2 in the base steel plate 1' is increased towards the inner direction of the base steel plate 1' instead of the direction of the interface (where the interface includes the interface of the iron oxide 3 and the base steel plate 1' and the interface of the reduced iron 4 and the base steel plate 1 '), so that the enrichment at the interface is inhibited, the effect of inhibiting the enrichment at the interface of the iron oxide 3 and the base steel plate 1' in the first heating stage is maintained, and the high dew point also has a certain promotion effect on inhibiting the enrichment at the surface of the steel plate.
When O is present 2 When the volume fraction of (b) is less than 0.01%, the oxidation degree of the base steel sheet 1 is too low to sufficiently suppress the surface enrichment of the steel sheet; when O is present 2 When the volume fraction of (b) is more than 0.5%, the oxidation degree of the base steel sheet 1 is too high, which is not favorable for the subsequent reduction and the coating adhesion. Thus defining O of the first heating atmosphere 2 The volume fraction is 0.01-0.5%。
When H is present 2 When the volume fraction is less than 0.5%, the reduction effect is insufficient, which is not favorable for subsequent hot dipping. Thus defining the second heating atmosphere and the soaking atmosphere 2 When the volume fraction is more than or equal to 0.5 percent, when H 2 When the volume fraction is more than or equal to 2 percent, the reduction effect is better, so the H of the second heating atmosphere and the soaking atmosphere 2 The volume fraction is preferably ≥ 2%.
When the dew point of the atmosphere is less than-20 ℃, the enrichment of the interface between the iron oxide 3 and the matrix steel plate 1 'and the interface between the reduced iron 4 and the matrix steel plate 1' can hardly be inhibited in the first heating stage, the second heating stage and the soaking stage, so that the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are limited to be more than or equal to-20 ℃.
Alternatively, the base steel sheet 1 contains 0.1 to 0.3% by mass of C, 0.5 to 3.0% by mass of Si, 0.5 to 4.0% by mass of Mn, and the balance being Fe and inevitable impurities.
The mass fraction of C is limited to 0.1-0.3% because the tensile strength of the steel sheet is insufficient when the mass fraction of C in the base steel sheet 1 is less than 0.1%, and the weldability of the steel sheet is deteriorated when the mass fraction of C in the base steel sheet 1 is greater than 0.3%. When the mass fraction of Si of the base steel sheet 1 is less than 0.5%, the tensile strength and elongation at break of the steel sheet are insufficient, and when the mass fraction of Si of the base steel sheet 1 is greater than 3.0%, the high temperature plasticity of the steel sheet is insufficient, increasing the defect occurrence rate at the time of processing, so the mass fraction of Si is limited to 0.5 to 3.0%. When the mass fraction of Mn of the base steel sheet 1 is less than 0.5%, the tensile strength and elongation at break of the steel sheet are insufficient, and when the mass fraction of Mn of the base steel sheet 1 is greater than 4.0%, the hardenability of the steel sheet is excessively high, which is not favorable for fine control of the structure, so that the mass fraction of Mn is limited to 0.5 to 4.0%.
Optionally, in the hot dip coating step, the temperature of the steel plate is 450-520 ℃ when the steel plate is put into a zinc pot, the temperature of the plating solution is 450-500 ℃, the plating solution contains 0.10-0.15% by mass of Al, and the balance of Zn and inevitable impurities, and the plating adhesion of each surface of the steel plate subjected to the hot dip coating step is 30-90g/m 2 。
After the hot dip coating, the cross section of the steel sheet is changed from that shown in fig. 2 (c) to that shown in fig. 2 (d), and a pure zinc coating layer 5 is formed on the steel sheet. When the zinc is put into a zinc potThe temperature of the steel plate and the temperature of the plating solution influence the reaction between the steel plate and the plating solution, when the temperature of the steel plate and the temperature of the plating solution in the process of entering the zinc pot are too low, the reaction speed is slow, the efficiency is reduced, when the temperature of the steel plate and the temperature of the plating solution in the process of entering the zinc pot are too high, the reaction speed is too fast, an explosive structure can be formed, and the control of the content of the plating Fe in the follow-up alloying process is not facilitated. Therefore, the temperature of the steel plate is 450-520 ℃ when the steel plate is put into a zinc pot for limited hot dip plating, the temperature of the plating solution is 450-500 ℃, the reaction speed is moderate when the temperature of the steel plate is 470-500 ℃ when the steel plate is put into the zinc pot, and the temperature of the plating solution is 460-480 ℃, so that the temperature of the steel plate is 470-500 ℃ when the steel plate is put into the zinc pot, and the temperature of the plating solution is 460-480 ℃ preferably. The plating solution contains 0.10 to 0.15% by mass, preferably 0.10 to 0.12% by mass, of Al. The zinc adhesion amount of each surface of the steel plate after the hot dip coating step is less than 30g/m 2 When the coating is used, the corrosion resistance is poor, and the zinc plating adhesion amount on each surface is more than 90g/m 2 In the process, the zinc-iron alloy coating 6 has poor formability, is easy to pulverize and fall off, influences the alloying process, and is not beneficial to the steel plate to obtain enough coating Fe content and high fracture elongation, so that the zinc coating adhesion amount of each surface of the steel plate subjected to the hot dip coating step is limited to 30-90g/m 2 。
Optionally, the temperature of the steel plate in the alloying treatment step is controlled to be less than or equal to 500 ℃ and the time is controlled to be less than or equal to 25 seconds.
After the alloying treatment, the cross section of the steel sheet is changed from that shown in FIG. 2 (d) to that shown in FIG. 2 (e), and Zn of the pure Zn plating layer 5 and Fe of the base steel sheet 1' are diffused into each other during the alloying treatment, thereby forming a Zn-Fe alloy plating layer 6 on the steel sheet. Because the temperature and the time of the steel plate in the alloying treatment step can influence the stability of the residual austenite and the Fe content of the coating, when the temperature of the steel plate is more than 500 ℃ or the time is more than 25 seconds, the stability of the residual austenite in the steel plate is reduced, the proportion of the residual austenite is reduced, the fracture elongation of the steel plate is reduced, and the zinc-iron diffusion degree is too high, and the anti-pulverization performance of the zinc-iron alloy coating 6 is deteriorated, the temperature of the steel plate in the alloying treatment step is less than or equal to 500 ℃ and the time is less than or equal to 25 seconds, and when the temperature of the steel plate is less than or equal to 480 ℃ and the time is less than or equal to 20 seconds, the proportion of the residual austenite in the steel plate is higher, and the fracture elongation of the steel plate is higher, the temperature of the steel plate in the alloying treatment step is preferably less than or equal to 480 ℃, and the time is preferably less than or equal to 20 seconds.
Optionally, the temperature of the steel plate in the alloying treatment step is controlled to be more than or equal to 460 ℃, and the time is controlled to be more than or equal to 5 seconds.
The temperature and the time of the steel plate in the alloying treatment step can influence the Fe content of the coating, and the temperature is less than 460 ℃ or the time is less than 5 seconds, so that the Zn and Fe are insufficiently diffused and the Fe content of the coating is insufficient, and the temperature of the steel plate in the alloying treatment step is limited to be more than or equal to 460 ℃ and the time is more than or equal to 5 seconds.
Optionally, the outlet temperature of the first heating stage is controlled to be in the range of 570-750 ℃.
The exit temperature affects the oxidation degree of the base steel sheet 1, when the temperature is less than 570 ℃, the oxidation degree of the base steel sheet 1 is too low to sufficiently suppress the surface enrichment of the steel sheet, when the temperature is more than 750 ℃, the oxidation degree of the base steel sheet 1 is too high to be beneficial to the subsequent reduction and the adhesion of the plating layer, so the exit temperature of the first heating stage is limited to 570-750 ℃, when the exit temperature is 600-720 ℃, the oxidation degree is moderate, and therefore the exit temperature of the first heating stage is preferably 600-720 ℃.
Optionally, the temperature of the steel plate in the soaking stage is controlled to be 750-930 ℃ for 30-300 seconds.
The temperature of the steel plate in the soaking stage influences the formation of austenite, when the temperature of the steel plate is less than 750 ℃, the austenitizing of the steel plate is insufficient, and when the temperature of the steel plate is more than 930 ℃, the steel plate can form coarse austenite grains which are unfavorable for the performance of the steel plate, so the temperature of the steel plate in the soaking stage is limited to 750-930 ℃. The soaking period is limited to 30-300 seconds, because the austenitizing of the steel sheet is insufficient when the soaking period is less than 30 seconds, and the production efficiency is affected when the soaking period is more than 300 seconds.
Optionally O of the first heating atmosphere 2 The volume fraction is 0.03-0.3%.
When the first heating atmosphere is O 2 When the volume fraction is 0.03 to 0.3%, the oxidation degree of the base steel sheet 1 becomes more moderate, so that O in the first heating atmosphere 2 The volume fraction is preferably 0.03 to 0.3%.
Optionally, H of a second heating atmosphere, soaking atmosphere 2 The volume fraction is less than or equal to 10 percent.
H of second heating atmosphere, soaking atmosphere 2 When the volume fraction is more than 10%, the reduction effect on iron oxide 3 does not increase, and the second heating atmosphere and the soaking atmosphere are defined by H from the economical point of view 2 The volume fraction is less than or equal to 10 percent.
Optionally, the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are controlled to be less than or equal to 30 ℃.
After the dew point is higher than 30 ℃, the inhibition effect on the enrichment at the interface between the iron oxide 3 and the base steel plate 1 'and the interface between the reduced iron 4 and the base steel plate 1' is not increased any more, so that the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are limited to be less than or equal to 30 ℃.
Optionally, the dew point of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere is controlled to be more than or equal to-10 ℃.
When the atmosphere dew point is more than or equal to minus 10 ℃, the effect of inhibiting the interface enrichment of the ferric oxide 3 and the matrix steel plate 1 'and the reduced iron 4 and the matrix steel plate 1' is obvious, so the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are preferably more than or equal to minus 10 ℃.
Optionally, the dew point of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere is controlled to be more than or equal to 0 ℃.
When the atmosphere dew point is more than or equal to 0 ℃, the effect of inhibiting the interface enrichment of the iron oxide 3 and the matrix steel plate 1 'and the reduced iron 4 and the matrix steel plate 1' is more obvious, so the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere are more preferably more than or equal to 0 ℃.
The invention also provides a hot-dip galvanized steel sheet prepared by the manufacturing method.
Optionally, the steel plate comprises a zinc-iron alloy coating 6 and an internal oxidation layer 2 from outside to inside, the zinc-iron alloy coating 6 contains 7-13% by mass of Fe, the proportion of the retained austenite phase in the structure is more than or equal to 5%, the tensile strength of the steel plate is more than or equal to 980MPa, and the fracture elongation is more than or equal to 20%.
The invention also provides a vehicle component which is made of the hot-dip galvanized steel sheet.
Examples
Examples 1 to 11 and comparative examples 1 to 6
Base steel sheets having the compositions shown in table 1 were selected, and the hot-dip galvanized steel sheets of examples 1 to 11 and comparative examples 1 to 6 were produced by the following production methods.
(1) A first heating stage: heating the base steel plate from ambient temperature to outlet temperature in an atmosphere of O 2 Atmosphere, balance N 2 And inevitable impurities, and controls the dew point.
(2) A second heating stage: heating the steel plate from the outlet temperature to the steel plate temperature of the soaking stage in the atmosphere of H 2 Atmosphere, balance N 2 And inevitable impurities, and controls the dew point.
(3) A soaking stage: keeping the steel plate at the temperature of H 2 Atmosphere, balance N 2 And unavoidable impurities, and controlling the dew point.
(4) A first cooling stage: and cooling the steel plate from the temperature of the steel plate in the soaking stage to the temperature of the steel plate when the steel plate is put into a zinc pot, wherein the cooling speed is more than or equal to 10 ℃/s.
(5) Hot dip plating: immersing the steel sheet in a plating solution maintained at a plating solution temperature and containing Al and the balance of Zn and inevitable impurities, wherein the amount of zinc attached to each surface of the steel sheet subjected to hot dip plating is 30-90g/m 2 。
(6) Alloying treatment: and controlling the temperature of the steel plate subjected to hot dip coating at the steel plate temperature in the alloying treatment step for heat preservation to form a zinc-iron alloy coating.
(7) And a second cooling stage: the steel sheet is cooled from the steel sheet temperature of the alloying treatment step to the ambient temperature.
Comparative example 7
A base steel sheet having the composition shown in table 1 was selected, and a galvanized steel sheet of comparative example 7 was produced by the following production method.
(1) A first heating stage and a second heating stage: heating the base steel plate from ambient temperature to the steel plate temperature in the soaking stage in the atmosphere of H 2 Atmosphere, balance N 2 And inevitable impurities, and controls the dew point.
(2) - (6) are the same as (3) to (7) of the production methods of examples 1 to 11 and comparative examples 1 to 6.
The performance test method comprises the following steps:
the hot dip galvanized steel sheet was subjected to performance tests as described in the following test methods, and the test results are shown in table 1:
(1) Tensile strength (MPa)
The test was carried out using a universal tensile tester, according to the method described in GB/T228.1-2010.
(2) Elongation at Break (%)
The test was carried out using a universal tensile tester, according to the method described in GB/T228.1-2010.
(3) Coating Fe content (%)
Selecting a wafer with the diameter of 50mm punched by a steel plate as a sample to be measured, dissolving a coating by using a hydrochloric acid solution which is added with a hexamethylenetetramine corrosion inhibitor and accounts for 10% by volume, and measuring the Fe content by adopting an ICP-AES method.
(4) Austenite phase ratio (%)
After the section metallographic phase is prepared, identifying and quantitatively analyzing each phase by using a scanning electron microscope back scattering diffraction device (EBSD), and calculating the phase proportion of the retained austenite.
The metallograph shooting method comprises the following steps:
the hot-dip galvanized steel sheet was photographed by metallographic imaging according to the following imaging method, and the photographs are shown in fig. 3 and 4:
after preparing a cross section metallographic phase, shooting by adopting a metallographic microscope.
Figure BDA0002598447960000111
Figure BDA0002598447960000121
The following is apparent from Table 1. As is clear from examples 1 to 11, the hot-dip galvanized steel sheet obtained by the production method of the present invention had a tensile strength of 980MPa or more, a coating Fe content of 7 to 13% by mass, and a breaking elongation of 20% or more. A steel sheet having a high Si and Mn content is used as a base material to obtain a high tensile strength and also to obtain a sufficient Fe content in a plating layer and a high elongation at break. Fig. 3 is a metallographic photograph of a cross section of the hot-dip galvanized steel sheet obtained in example 1, and it can be seen that the zinc-iron alloy plating layer was sufficiently alloyed, and the internal oxidation layer formed by the Si and Mn alloy elements was thick, indicating that the enrichment degree of the steel sheet surface and the interface between the iron oxide and the base steel sheet, and the interface between the reduced iron and the base steel sheet was low.
As for comparative example 1, it was O in the first heating stage 2 The content is insufficient, so that the oxidation degree of the base steel plate is insufficient, the inhibition effect of iron oxide on the enrichment of Si and Mn alloy elements on the surface of the steel plate is poor, the Si and Mn alloy elements form continuous oxides on the surface of the steel plate and influence the alloying speed, so that the alloying temperature is increased to 550 ℃, the alloying time is prolonged to 30s, the austenite content is reduced, and the fracture elongation of the steel plate is only 17%.
As for comparative example 2, the dew point at the first heating stage was too low at-30 ℃, resulting in deterioration of the inhibition effect of the dew point on the enrichment of Si, mn alloy elements, especially the inhibition effect on the enrichment of the interface of iron oxide and the base steel sheet, and Si, mn alloy elements formed continuous oxides at the interface, affecting the alloying speed, so that the alloying temperature was increased to 530 ℃, resulting in a decrease in the austenite content, a steel sheet elongation at break of only 14.7%, and a plating iron content of still only 3.7%.
In comparative example 3, the exit temperature in the first heating stage was too low, only 550 ℃, resulting in insufficient oxidation degree of the base steel sheet, poor inhibition of the enrichment of the Si and Mn alloy elements on the steel sheet surface by iron oxide, formation of continuous oxides of the Si and Mn alloy elements on the steel sheet surface, affecting the alloying rate, and the coating iron content was only 5.2%.
As comparative example 4, it was O in the first heating stage 2 The content is too high, so that the oxidation degree of a parent steel plate is too high, the subsequent reduction is not thorough, the adhesion of a plating layer is poor, the temperature of the plating solution in the hot dip plating step is too low, only 360 ℃, so that the reaction between the plating solution and the steel plate is poor, the alloying temperature is increased to 510 ℃, so that the austenite content is reduced, the fracture elongation of the steel plate is only 18.8%, and the iron content of the plating layer is still only 2.5%.
With respect to comparative example 5, the dew point at the second heating stage was too low at-25 ℃, resulting in deterioration of the inhibitory effect of the dew point on the enrichment of the Si, mn alloying elements, and particularly on the enrichment of the interface (where the interface includes the interface of iron oxide with the base steel sheet and the interface of reduced iron with the base steel sheet), and the Si, mn alloying elements formed continuous oxides at the interface, affecting the alloying rate, so that the iron content of the plating layer was only 3.4%.
In comparative example 6, the dew point at the soaking stage was too low at-25 ℃ to deteriorate the inhibitory effect of the dew point on the enrichment of the Si, mn alloy elements, and particularly on the enrichment at the interface (where the interface includes the interface of iron oxide with the base steel sheet and the interface of reduced iron with the base steel sheet), and the Si, mn alloy elements formed continuous oxides at the interface to affect the alloying rate, so that the iron content of the plating layer was only 2.8%.
With respect to comparative example 7, the first heating stage was an H2 atmosphere instead of O 2 The atmosphere does not form an iron oxide layer, and an interface between the base steel plate and the iron oxide or reduced iron does not exist, so that the enrichment of Si and Mn alloy elements is not inhibited, the alloying speed is influenced, the alloying temperature is increased to 550 ℃, the austenite content is reduced, the fracture elongation of the steel plate is only 16%, and the iron content of the plating layer is still only 2.3%. FIG. 4 is a metallographic photograph showing the cross section of a hot-dip galvanized steel sheet obtained in comparative example 7, in which the alloying of the Zn-Fe alloy coating was insufficient and the internal oxidation layer formed by the Si and Mn alloy elements was thin, indicating that the surface of the steel sheet was heavily enriched.
In summary, according to the method for manufacturing the hot-dip galvanized steel sheet provided by the invention, through atmosphere control in the heating and soaking stages, enrichment of Si and Mn alloy elements on the surface of the hot-dip galvanized steel sheet is inhibited, and enrichment of Si and Mn alloy elements on the interface between iron oxide and the base steel sheet and the interface between reduced iron and the base steel sheet is inhibited, so that when the hot-dip galvanized steel sheet selects a steel sheet with high Si and Mn content as a base material, appropriate temperature and time of the steel sheet can be selected in the alloying treatment step, thereby facilitating obtaining of sufficient coating Fe content and high elongation at break, and being suitable for vehicle components.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims (14)

1. A method for producing a hot-dip galvanized steel sheet, comprising a heat treatment step, a hot-dip coating step and an alloying treatment step of a base steel sheet containing, by mass, at least 0.5% of Si and at least 0.5% of Mn,
the heat treatment step includes a first heating stage and a soaking stage, wherein,
the first heating atmosphere of the first heating stage contains 0.01-0.5% of O by volume fraction 2 The remainder being N 2 And inevitable impurities, the soaking atmosphere of the soaking stage contains more than 0.5 percent of H by volume fraction 2 The balance being N 2 And unavoidable impurities;
the heat treatment step further comprises a second heating stage in which a second heating atmosphere contains H in a volume fraction of 0.5% or more 2 The balance being N 2 And unavoidable impurities;
and controlling the dew points of the first heating atmosphere, the second heating atmosphere and the soaking atmosphere to be more than or equal to-10 ℃.
2. The manufacturing method according to claim 1, wherein the base steel sheet contains, by mass, 0.1 to 0.3% of C, 0.5 to 3.0% of Si, 0.5 to 4.0% of Mn, and the balance being Fe and unavoidable impurities.
3. The production method according to any one of claims 1 to 2, wherein in the hot dip coating step, the temperature of the steel sheet when put into a zinc pot is 450 to 520 ℃, the temperature of the plating solution is 450 to 500 ℃, and the plating solution contains 0.10 to 0.15% by mass of Al, and the balance being Zn and unavoidable impurities, and the hot dip coating is completedThe zinc plating adhesion amount of each side of the steel plate in the dip plating step is 30-90g/m 2 。
4. The production method according to any one of claims 1 to 2, wherein the steel sheet temperature of the alloying treatment step is controlled to 500 ℃ or less for 25 seconds or less.
5. The manufacturing method according to claim 4, wherein the temperature of the steel plate in the alloying treatment step is controlled to 460 ℃ or more for 5 seconds or more.
6. The manufacturing method according to any one of claims 1 to 2, characterized in that the outlet temperature of the first heating stage is controlled to be 570-750 ℃.
7. The manufacturing method according to any one of claims 1 to 2, wherein the temperature of the steel sheet in the soaking stage is controlled to 750 to 930 ℃ for 30 to 300 seconds.
8. The production method according to any one of claims 1 to 2, wherein O of the first heating atmosphere 2 The volume fraction is 0.03-0.3%.
9. The manufacturing method according to claim 1, wherein the second heating atmosphere, the H of the soaking atmosphere 2 The volume fraction is less than or equal to 10 percent.
10. The method according to claim 1, wherein the dew points of the first heating atmosphere, the second heating atmosphere, and the soaking atmosphere are controlled to be 30 ℃ or less.
11. The method according to claim 1, wherein the dew points of the first heating atmosphere, the second heating atmosphere, and the soaking atmosphere are controlled to be 0 ℃ or higher.
12. A hot-dip galvanized steel sheet produced by the production method according to any one of claims 1 to 11.
13. The hot-dip galvanized steel sheet according to claim 12, wherein the steel sheet comprises a zinc-iron alloy coating layer and an internal oxide layer from outside to inside, the zinc-iron alloy coating layer contains 7-13% by mass of Fe, the proportion of retained austenite in the structure is not less than 5%, the tensile strength of the steel sheet is not less than 980MPa, and the elongation at break is not less than 20%.
14. A member for a vehicle, made of the galvanized steel sheet according to any one of claims 12 to 13.
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